How to hack a cheap Casio into a real dive watch

The Casio F-91W is, famously, the only watch worn by Osama and Obama. As a beater it can’t be beat an, as David Tinarenco writes, it’s even better if you put it on a NATO strap. But what about that pesky water resistance?

Tinarenco has a solution: he basically fills the watch with mineral oil, thereby improving the pressure resistance to 1000+ PSI.

Fluids are said to be â€œvirtually incompressible.â€ Generally speaking, a gas (like air) is compressible: when pressure increases, volume decreases. The compressibility factor Î²
may be expressed as
Î²=âˆ’1Vâˆ‚Vâˆ‚p
where V
is volume and p
is pressure. A trick to achieve incredible depth ratings has been to submerge the internals of a watch in inert, non-reactive, non-corrosive, non-polar liquids. Mineral oil (a byproduct of petroleum refinement) is a fantastic choice â€” and this is exactly what Iâ€™ll be doing to my Casio F-91W. Theoretically, as water pressure increases around the watch, due to the fact that itâ€™s filled with an incompressible liquid (as opposed to a compressible gas), it can successfully â€œpush backâ€ against the water and it will not succumb to implosion due to increasing pressures.

Obviously this does a few things to the watch including make the backlight unusable and most probably voids the warranty but it’s a great little hack. Interestingly, this has been tried with a number of G-Shocks with similarly spectacular results. Maybe we should cut open our Rolexes next and fill them with olive oil?